1. Field of the Invention
This invention relates to film punches, particularly for providing multiple films such as color separations with punch register after exposure.
2. Description of the Prior Art
One type of film punch manufactured by the applicants, has an illuminated platform capable of accepting a maximum film size of 60.times.50 cm and punching heads which are inverted for operation from below upwards. A key film, usually that representing the blue separation or that with the most detail, is selected and placed on the platform over the punching heads, which are operated to perforate the film. The punching heads are brought to a position in which the punches project into, and are retained within the thickness of the key film to provide a positive location. Then the next separation is placed over the key film, slid over the punching heads, registered visually to the key film and the punching heads are operated to perforate the second film. The second separation is removed and the same procedure is repeated for the remaining color separations, after which the key film is released by depressing the punching heads to their original position.
Colour separations have, for some time, been produced on electronic scanners. Early electronic scanners were mostly single-channel and produced color separations one color at a time, so that color sets could be produced in register much the same as on a camera, by fitting the film drum with register pins. This enabled four separate pieces of film to be punched and placed in turn on the pins on the drum.
However, multi-channel scanners are now in operation. A four-channel scanner has the original film transparency fitted to one drum and the four-color separations are produced on a single piece of film, as shown in FIG. 1, of the accompanying drawings. One multi-channel scanner can produce register lines on the film that are in register with each separation. Further, if register crosses are included with the original transparency, for example by adhering the crosses thereto, then after the scanning operation they will appear against each separation.
Attempts have been made to produce a film punch that in addition to punching holes 1, 2, 3 and 4 adjacent illustrations A and B, will punch holes 5, 6, 7 and 8 in the correct relationship to illustrations C and D. However, due to the very close tolerances required, plus the movement of the film due to the temperature and humidity changes, this approach has not been successful.
The only practical method at the present time which is known to the applicants is to cut the film into four pieces and use the film punch previously described to introduce a pair of holes for each illustration using one of them as a key. However, such a method still relies upon operators having acute vision, who must maintain that vision throughout the entire working day for accurate punch registration.